The formation of underground impermeable barriers using slurry trench techniques has been widely developed in recent years and in a number of instances, attempts to utilize impervious plastic or rubber sheets to form impermeable barriers in such cut-off walls has been attempted. In Ranney U.S. Pat. No. 2,048,710, a pair of lining materials such as fabric or paper or other lining material which has been treated so that the lining material acts as a separator or divider between the earth material and the wall material after the wall material has been placed in the trench. In Zakiewicz U.S. Pat. No. 3,603,099, an intraground water proof baffle is disclosed in which the roll of flexible water proof plastic foil is displaced along the line of the excavation so that as the trench is cut, the foil is layed in a vertical plane behind the excavator and then the space between the foil and the sides thereof is filled with a wall forming material. In Piccagli U.S. Pat. No. 4,193,716 and Carron et al U.S. Pat. No. 3,759,044, plastic sheets are embedded in diaphram walls. These processes and structures are not amenable to the placement of such synthetic plastic materials in deep excavation using the slurry wall construction technique. In Ressi application Ser. No. 252,676, filed Apr. 9, 1981 and assigned to the assignee hereof, a plastic sheath or envelope is provided in which the wall forming material is in the sheath or envelope.
A pollution control barrier according to a preferred embodiment of the present invention comprises a narrow slot excavated in the earth using the bentonite slurry technique as disclosed in Veder U.S. Pat. No. 3,310,952, such that the earthen walls are impregnated with bentonite and a bentonite cake is formed on the surfaces thereof. A plastic sheet is inserted in the slot and, preferrably, is aligned with the center of the slot and a wall forming material fills the slot on both sides of the plastic sheet. An important feature in the present invention is in that the plastic sheeting is in panel sections as follows: a first series of the panel sections having vertical plastic primary tubes or channels bonded to the lateral ends, respectively, of the plastic sheet, each said plastic tube or channel having a diameter at least equal to the width of the slot in the earth with the ends of the plastic sheet fusingly bonded to one side, respectively, of each said tube in a fluid impervious manner. Each of the vertical plastic tubes or channels has a slit or elongated opening in the opposite side to which the plastic sheeting is bonded. A second series of panel sections, alternating with the first series of primary panel sections along the line of the wall are constituted by a further plastic sheeting with secondary pipe or channel members secured to the ends of the sheet, the secondary pipe or channel members having a diameter or size small enough to telescope within the first tubes with the plastic panel sheeting passing through the slits or elongated openings, respectively, in the primary tube or channel members and finally, a grouting means fills all of the voids in the tubes or channels displacing any bentonite that may have seeped therein. The grout is a non-shrink type and is pumped into the joint connection to form a tight joint. The resulting wall has chemical resistivity and lower permeability. In addition, it allows the synthetic material to be placed in deep excavations using slurry wall construction methods and the joints will allow for a continuous impervious wall system. It is simpler and easier to install in short panel sections. Different sections of the impervious wall can be tailored to have different properties. The cut-off made according to the present invention can be used for deep excavations (at least over 70 feet deep) and still be continuous.